> I have a client who is experiencing something rather strange. Every few > seconds, and not with any particularly regularity, "topas" will report a > spike in disk writes, maxing out one or more disks to 100% utilization. CPU > utilization, on the other hand, remains nominal or only slightly elevated. > When this happens, the world stands still - literally - as user screens > freeze up until several seconds after the disks have gone back to normal > load.
It may be tied to the syncd daemon, depending on how frequently "every few seconds" is. Try fiddling with the maxrandwrt parameter of the ioo command. I've seen this work miracles with intermittent spikes like you're describing. (I've also seen it make no difference at all, depending on the circumstances.) The default behavior of AIX provides improved overall system performance, but sometimes interactive processes suffer. By using the write-behind buffer with maxrandwrt, you even things out and reduce the spiky performance. Anyway, check out the man page for ioo and search for maxrandwrt for more information. This would probably be the easiest thing to try first. If it doesn't provide relief, you may want to play around with filemon, as suggested by somebody else. It will show you the busiest files on the system, but requires tinkering with quite a few command-line parameters to get useful results. Of course, AIX and UniData tuning can be quite complex, and the problems could be due to any number of factors. If no relief is in sight, you may need to get some assistance from somebody with experience with this type of tuning. [Oops - I forgot to enable the shameless plug alert.] Tim Snyder Consulting I/T Specialist U2 Lab Services Information Management, IBM Software Group ------- u2-users mailing list u2-users@listserver.u2ug.org To unsubscribe please visit http://listserver.u2ug.org/
